The United States Secret Service is in dire need of an overhaul that requires an outside leader, an infusion of agents and more training to protect the White House, an independent review has concluded.

An executive summary of the highly classified review revealed deep problems at the top of the Secret Service, which is charged with guarding the US president and other senior government officials.

"Some of the changes address isolated problems, with well-defined options to solve them, while others will require far more study by, we hope, a dynamic new management team that will lead the Service into the future," the summary said.

Homeland security secretary Jeh Johnson appointed the four-member review panel in October after the September 19 intrusion by an Iraq war veteran with a knife who scaled the White House fence, sprinted across the lawn and got deep inside the mansion before an off-duty agent stopped him.

That incident prompted the panel's first recommendation of building a better fence "as soon as possible".

It recommended one that is at least 120 or 150 cm higher and curves outward at the top to give agents more time to assess the risk of a jumper.

But the agency's problems, it noted, "go deeper than a new fence can fix".

New leadership is crucial for driving change within an agency that it described as highly insular.

A director not tied to agency traditions and personal relationships will be better equipped to do an honest reassessment and encourage a culture of accountability.

The last Secret Service director, Julia Pierson, resigned under fierce criticism on October 1.

The fence jumper breach came a day after the disclosure that an armed private security contractor with a criminal record rode on an elevator with Mr Obama in Atlanta, a breach of protocol, earlier in September.

The panel said the agency would also require more special agents and uniformed division personnel who work an "unsustainable number of hours".

"The Secret Service is stretched to and, in many cases, beyond its limits," the panel said.

It said the report tried to quantify how many more agents were needed but has lacked complete data.

The agency's training regimen has diminished far below acceptable levels, it found, with the average special agent receiving only 42 hours of training.

"The panel's recommendations are astute, thorough and fair," Mr Johnson said in a statement.

The security lapses, along with a 2011 incident in which seven gunshots were fired at the White House, had raised concerns across Washington that Mr Obama was not as well protected as he should be in an age of global tumult.